This invention relates to devices for retrieving and deploying lengths of cable, particularly to devices for manipulating umbilical cables which serve as controls or tethers for underwater devices, and most particularly to linear cable engines which are designed for gripping an umbilical cable during transport without damaging the cable by providing a gripping mechanism which encompasses the cable and applies pressure radially thereto.
Linear cable engines (LCE), as referred to herein are not engines, but rather refer to a linear winch or tensioning device for cable. Rather than spooling the cable up on a drum as a conventional winch does, a LCE allows the cable to pass through in a straight line and continue on to another device or alternatively deployed overboard.
There are generally two types of LCE in use today: multi-tire and track.
The multi-tire system consists of a series of vertically mounted truck tire/wheel combinations, all of which are powered with hydraulic motors. Each pair roll on one another with the cable passing between them passing the cable to the next pair. These matched pairs are mounted on a long frame and the number of tire pairs is determined by the desired tension.
The track system consists of a pair of rubber or polymeric tracks mounted similarly to the tire system. These tracks are also hydraulically powered as the multi-tire system. Some manufacturers of the track systems will have a semicircular indention in the track to accommodate the cross section of the cable being handled. Either of these systems are used to lift the product cable from a holding tank on the cable lay ship and feed it overboard if no installation tension is needed. If the product cable requires back tension or the recovery of a previously laid cable is required, the LCE provides back tension for a capstan winch (better known as a cable drum engine). The cable lay ships carry all this equipment as they must be prepared for any type of circumstance as well as many types of product cable.
The Multi-tire LCE was the first concept to gain wide industry acceptance. One of the main problems with this system is that it takes up valuable deck space as many pairs of tires are required to develop the tensions required. Additionally, this system does not guide the cable well thus alignment is very critical. Furthermore, multi-tire LCEs often strip the protective sheath from the product cable in times of high tension requirements. Such systems are a maintenance problem as there are many hydraulic motors along with their corresponding plumbing necessary, they are difficult to keep xe2x80x9cin tunexe2x80x9d as there are many pairs that must stay in time to xe2x80x9cshare the loadxe2x80x9d .
With regard to Track type LCEs, these systems improve upon the multi-tire systems in that they better utilize deck space, are typically capable of applying higher tensions, utilize less hydraulic motors and require less plumbing for a given tension rating, are less susceptible to alignment problems as the tracks have a wider contact surface, can be produced with a groove aligned in the cable travel direction adding to the available xe2x80x9ccable gripxe2x80x9d, and are used sub-sea in combination with the latest technology sea plows. This system also suffers, however, in that it often strips the protective sheath from the product cable in times of high tension requirements.
U.S. Pat. No. 4,508,251 discloses a cable pulling/feeding apparatus having a fixed base, a cable pulling/feeding unit inclusive of a drive/brake unit for pulling or feeding a cable, a load detecting sensor, and structure for determining a load applied to the drive/brake unit in response to a signal to pull or feed the cable. The patent fails to apply radial pressure to the cable, as instantly disclosedxe2x80x94see particularly FIG. 4.
U.S. Pat. No. 5,009,353 discloses a cable tensioner having a pair of elongated platforms in side-by-side relationship for driving the cable. Belts, formed from a high friction material are designed with a groove therein to match the diameter of the cable. This patent, although applying pressure about the cable""s circumference, does so by pressing the two gripping halves together, and thus also fails to disclose a gripping element which utilizes radially applied pressure to evenly grip the belt.
U.S. Pat. No. 5,082,248 provides an apparatus for pulling on a line. A drive pulley with a circumferential groove is provided and a loop of the line is held therein. A radial cable gripping element is not disclosed in the patent.
U.S. Pat. No. 1,759,105 provides a die for laying wire rope and wire rope strands. The die elements on opposing chains come together to provide a gripping force. Again, this device fails to teach a gripping element which generates radial pressure upon the wire/cable.
U.S. Pat. No. 3,275,300 teaches a device for transporting conduit in a well drilling environment wherein pairs of clamps are brought together as they are articulated on shackles which are attached to endless chains. The clamps grip the conduit and urge it along in the direction of rotation of the endless chains. The device fails to teach a gripping element which generates even radial pressure upon the wire/cable.
What is lacking in the prior art is a cable umbilical gripping device having a gripping element which utilizes radially applied pressure to evenly grip the cable. In a particularly preferred embodiment the gripping device includes a deformable polymeric gripping element which aids in applying even gripping and transfer of tension to the cable. The ability to provide even tension upon the cable as a result of deformation of the polymeric or gel-filled blocks significantly reduces cable wear and damage.
The instant invention teaches an LCE which uniquely grips a cable, e.g. a marine umbilical cable, so as to avoid damage to the protective/insulative sheath thereon. The LCE as described in the instant invention includes either a track or tire type LCE having a design which encompasses the cable and actually applies pressure radially to the cable. This allows for the application of much higher force as the cable is in a state of hydrostatic stress resulting in a higher allowable tension on the cable.
The currently available designs either use a flat track or an indented track. While the indented track increases the contact surface to the cable, it, like the flat track, only applies pressure to the cable in one direction. This limits the amount of force that can be applied before internal damage occurs in the cable due to Poisson""s effect.
In accordance with the instant invention, the tracks are modified from a smooth continuous belt to a smooth or segmented continuous belt, a chain, or the like conveying means containing polymeric blocks attached to the outer surface. Each block is identical in shape and construction. The blocks have a semi-circular indention that matches a given cable radius and a hollow (air-filled) cross-section or deformable media filled, e.g. a gel-filled cross-section with optional strategically placed stiffeners. When the cable is squeezed between the two tracks, the sidewalls of the block are pulled towards the cable creating a horizontal loading.
The benefit achieved by the instant LCE is that the LCE can be used at higher tensions for a given cable or less LCE""s can be used for a given tension resulting in less required deck space. Both of these are due to the fact that a better grip on the cable will allow better transfer of tension to the cable and raise the tension at which damage might occur.
Accordingly, it is an objective of the instant invention to teach an LCE wherein the tracks are modified to contain polymeric blocks bolted to the outer surface of the track; each block being identical in shape and construction.
It is an additional objective of the instant invention to teach a tire type LCE wherein the circumferential surface of the tire is modified to present an elastomeric profiled surface effective to embrace the cable.
It is a further objective of the instant invention to teach a modified LCE wherein the blocks have a semi-circular indention that matches a given cable radius and a hollow cross-section or deformable media-filled cross-section which may further contain strategically placed stiffeners.
It is yet another objective of the instant invention to teach an LCE and method for its use, which can be used at relatively higher tensions, compared to prior art LCEs, for a given cable, or less LCE""s can be used for a given tension resulting in less required deck space; due to the fact that a better grip on the cable will allow better transfer of tension to the cable and raise the tension at which damage might occur.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.